The present invention relates to a rotary damper for applying damping forces to, for example, a door or a cover when the door or the cover is opened or closed.
A conventional rotary damper 1 as shown in FIG. 15 has a ridge member 15 provided on an outer circumferential surface of a proximal portion 5 of a rotatable member 4 and a land 11 provided on an inner circumferential surface of a chamber 3. When the rotatable member 4 rotates to a high torque production side (in the clockwise direction in the drawing), the pressure of a viscous fluid 7 increases in a compression compartment 3a of the chamber 3, by which a high torque is obtained.
Also, a conventional rotary damper disclosed in Japanese Patent Laid-Open No. 2000-46087, as shown in FIG. 16, has a construction such that a substantially cylindrical sleeve 5 made of a synthetic resin is disposed between an inner end face 21a of a partition wall portion 21 of a casing 2 and the outer circumferential surface of a rotating shaft 3 provided with a vane member 4. Such a sleeve 5 can prevent a gap from developing between the inner end face 21a of the partition wall portion 21 of the casing 2 and the outer circumferential surface of the rotating shaft 3 because it absorbs irregularities on the inner end face 21a of the partition wall portion 21 by means of the elastic force thereof. As a result, even when a viscous fluid with allow viscosity is used, a high torque can be produced.
However, what we call a one-blade rotary damper having one ridge member 15 as shown in FIG. 15 has a problem described below. When the rotatable member 4 rotates to the high torque production side to increase the pressure of the viscous fluid 7 in the compression compartment 3a, the proximal portion 5 of the rotatable member 4 rotates eccentrically in the direction indicated by the arrow mark in FIG. 15, so that a clearance between the outer circumferential surface of the proximal portion 5 and the inner end face of the land 11 increases. Thereby, a bypath flow of the viscous fluid 7 from the clearance, which is only of a negligible amount intrinsically, is increased, so that the torque in the high torque production region decreases. As a result, sufficient damping action necessary when a door etc. provided with the rotary damper is closed cannot be accomplished.
Also, the rotary damper shown in FIG. 16 has a problem described below. The long-term use of the rotary damper develops a gap between the inner end face 21a of the partition wall portion 21 and the sleeve 5 by means of abrasion, so that the viscous fluid leaks from between the slidingly contacting surfaces of the rotating shaft 3 and the sleeve 5. As a result, the torque in the high torque production region decreases.
Accordingly, an object of the present invention is to provide a rotary damper in which even if the rotary damper is used for a long period of time, a clearance between the inner end face of partition wall and the outer circumferential surface of rotating shaft can be in a given range, whereby the torque in the high torque production region can be prevented from decreasing.
To solve the above problems, the present invention provides a rotary damper comprising a casing having a chamber defined therein; a viscous fluid filled in the chamber; a rotatable member being relatively rotatable with respect to the casing, the proximal portion of the rotatable member being accommodated in the chamber, a ridge member extending axially along and projecting radially outwardly from an outer circumferential surface of the proximal portion of the rotatable member, said ridge member having a radially outer end face disposed for sliding contact with an inner circumferential surface of the chamber; and a land extending axially along and projecting inwardly from said inner circumferential surface of the chamber, the land having a transverse face transversely with respect to rotational direction of the rotatable member, the ridge member and the land dividing an interior of the chamber into a compression compartment and a decompression compartment, the volume of the compression and decompression compartments being variable complimentarily to each other in response to the relative rotation of the rotatable member and the casing, a spacer interposed between the land and the proximal portion of the rotatable member and adapted to be pressed against the outer circumferential surface of the proximal portion of the rotatable member and the transverse face of the land by the pressure built up in the compression compartment in response to rotation of the rotatable member.
Even if a spacer portion on the outer circumferential surface side of the proximal portion of the rotatable member is worn by the long-term use of the rotary damper, the spacer can be pressed against the outer circumferential surface of the proximal portion of the rotatable member and the transverse face of the land by the pressure built up in the compression compartment.
In the present invention, a side face on the side of the compression compartment of the land forms the transverse face, and the spacer is disposed so as to cover the inner end face and the side face of the land. Therefore, since the spacer is disposed so as to straddle the land, the spacer does not come off from the land under the pressure on the compression compartment side.
In the present invention, the spacer has a portion along the side face of the land and such portion has an end face confronting the inner circumferential surface of the chamber to keep a gap therebetween. Thereby, the spacer can be press against the outer circumferential surface of the proximal portion of the rotatable member and the side face of the land by the pressure built up in the compression compartment in such a manner as to float from the inner end face of the land.
In the present invention, the land is provided with an inward protrusion on the inner end face thereof, a side face on the side of the compression compartment of the inward protrusion forms the transverse face, and the spacer is mounted on the inner end face of the land while engaging with the inward protrusion. Therefore, since the spacer is disposed so as to engage with the inward protrusion, the spacer does not come off from the land under the pressure on the compression compartment side.
In the present invention, the spacer has a portion on the side of the compression compartment, such portion has an end face confronting the inner end fare of the land to keep a gap therebetween. Thereby, the spacer is pressed against the outer circumferential surface of the proximal portion of the rotatable member and the inward protrusion by the pressure built up in the compression compartment in such a manner as to float from the inner end face of the land.
In the present invention, the spacer is made from at least one of a group consisting of plastic, rubber-like material and metal. By forming the spacer of such a material, the spacer can be pressed reliably against the outer circumferential surface of the proximal potion of the rotatable member and the transverse of the land by the pressure built up in the compression compartment.
In the present invention, the plastic material is a fluorine-containing plastic material. This offers an advantage that friction between the outer circumferential surface of the proximal portion of the rotatable member and the spacer can be decreased.